Diets, doubts, and doughnuts: are we truly clueless?

No, we are not, absolutely not, emphatically not clueless about the basic care and feeding of Homo sapiens. The fundamental lifestyle formula, including diet, conducive to the addition of years to our lives, and life to our years, is reliably clear and a product of science, sense, and global consensus. Really. You can be confused about it if you want to be, but I advise against it. You will be procrastinating, and missing out- because healthy people have more fun.

In the New York Times this past week, Gina Kolata made the case that almost all studies about diet, exercise, and health are suspect in 1 way or another, and that therefore we are confused about lifestyle practices for health, and justifiably so. The first point is valid; the second is utter nonsense. Let's take them in turn.

The contention that all research addressing lifestyle practices for health is limited in some way is certainly true, to the point of being both trivial and trite. All research is limited in some way; the perfect study has never been conceived, let alone executed. But we have nonetheless used research to produce very tangible results that prove the utility of our imperfect methods. We have put footprints on the moon; eradicated smallpox; put a spaceship in orbit around Jupiter; and routinely shoot perfectly clear messages to one another by jiggling electrons in cyberspace. Anyone exploiting the tools of modern living is a living illustration that research, though ineluctably flawed, works pretty darn well.

There is, moreover, a case to make that research addressing lifestyle practices may be especially prone to important limitations. If we consider that the pinnacle of evidence in human research is, generally, the randomized, double-blind, placebo-controlled trial, the challenges are immediately clear. How do you pair exercise, or an optimal diet, with some “placebo control,” while keeping your study participants blind to their treatment assignment? How can we have some people exercise, and others not, without them picking up on it? We cannot.

But that's just the start of our tribulations with such trials. Consider an effort to determine if, say, an optimal Mediterranean diet is better or worse for human health than an optimal vegan diet, or an optimal Paleo diet. The ultimate outcome of interest, healthy survival, is a product of both longevity and vitality. To address longevity, we need very long trials. Years won't do; we are talking decades.

Now, we must allow for the fact that lifestyle influences health throughout the lifespan. If we want to know what diet is best for health, we should therefore look across the entire lifespan. That means starting young. In fact, even young isn't early enough, because dietary effects begin in utero. There is even a case for them beginning with our grandparents, but we will let that epigenetic influence go for the sake of pragmatism.

Still, to study the lifelong effects of diet on health, we would need to randomize a very large cohort of pregnant women to different dietary patterns. The women would need to be alike in all ways but diet. They would need to adhere to their dietary assignment throughout pregnancy, then proceed to breast feeding, and adhere then as well. After that, as the large crop of infants is weaned from breast milk, those neonates would become the study participants, and it would be their turn to adhere to the dietary assignment- forever. After some span of decades, and the expenditure of a staggering sum, we would be able to look at differences in health outcomes, and perhaps attribute them to our intervention if too many other things were not now different between our groups.

I trust you understand why such a trial has not been conducted, and why you shouldn't hold your breath waiting for it. That leaves us with the lesser standards of research against which Ms. Kolata has chosen to inveigh.

But that does not leave us clueless, any more than the lack of a randomized comparison of treatment versus benign neglect is required to know that bullet holes through peoples' chests warrant emergency surgery. We have no randomized trials telling us that water puts out most fires, and yet our firefighters carry on as if they know what they are doing. We had no perfectly unassailable proof that we could put a spaceship into orbit around Jupiter, until we went ahead and based on imperfect science, did exactly that.

What we have done in all areas where science has proven its inimitable utility is look at the weight of evidence, and apply sense. That formula is vastly more powerful, useful, and nearly perfect than any one study has ever been.

In the case of lifestyle for health, the formula works perfectly well despite the research imperfections that trouble Ms. Kolata. She is quite right to recommend a raised eyebrow about any 1 study, and in particular, the hyperbolic headlines it is likely to engender. But look instead at the weight of evidence, encompassing randomized trials, mechanistic studies, observational epidemiology, and real-world experience at the level of whole populations- and you generate a rather emphatic mandate to keep that restless eyebrow at its low-altitude ease.

Consider the implications for yourself, and for that matter Ms. Kolata, if the lack of “perfect” research really made us clueless about diet. We would have no idea whether lentils or lollipops were a better source of sustenance. We could not judge the differential merits of dates, and jelly doughnuts. We would not know whether oatmeal and walnuts, or Doritos and Coca Cola made a better breakfast.

I very much doubt that Ms. Kolata has any difficulty judging the relative merits of kale and cheese doodles. But once we are in for that penny, we are in for a pound. If we know, despite our research imperfections, that broccoli is generally a terrific choice, and baloney not so much, then we clearly have a basis to understand something in spite of it all. There is no reason for that understanding to end with baloney, and indeed it does not. We, and Ms. Kolata, all make confident choices every day, informed by science, guided by sense.

No single study, about diet or anything else, is perfect. If that gets you exercised, go ahead and exercise your derisive eyebrow as Ms. Kolata advises. But on the other hand, the massive weight of evidence in the aggregate tips clearly and decisively. A global consensus of expert judgment concurs. Sense, applied a bit too seldom to be called “common,” alas, aligns. Routine physical activity and a diet of mostly minimally processed vegetables, fruits, whole grains, beans, lentils, nuts, seeds and water when thirsty redounds consistently to the advantage of human health. It offers benefits to the planet as well.

I recommend that you leave your eyebrow just where it is, and lift instead your feet, and your fork, accordingly.

David L. Katz, MD, FACP, MPH, FACPM, is an internationally renowned authority on nutrition, weight management, and the prevention of chronic disease, and an internationally recognized leader in integrative medicine and patient-centered care. He is a board certified specialist in both Internal Medicine, and Preventive Medicine/Public Health, and Associate Professor (adjunct) in Public Health Practice at the Yale University School of Medicine. He is the Director and founder (1998) of Yale University's Prevention Research Center; Director and founder of the Integrative Medicine Center at Griffin Hospital (2000) in Derby, Conn.; founder and president of the non-profit Turn the Tide Foundation; and formerly the Director of Medical Studies in Public Health at the Yale School of Medicine for eight years. This post originally appeared on his blog at The Huffington Post.

Internal medicine physicians are specialists who apply scientific knowledge and clinical expertise to the diagnosis, treatment, and compassionate care of adults across the spectrum from health to complex illness.
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